The effect of sex hormones on collagen and elastin turnover and accumulation in aortae of rats will be determined. In addition, blood pressure and mechanical properties of vessels will be determined in these same animals. In phase 1 both castrated and non-castrated male rats are injected with estradiol, testosterone, or oil. At the end of 3 weeks, C14 proline is injected into each rat and rats are killed at 3 hours, 2 days, 7 days and 3 weeks after injection of the radioactivity. Specific activity of hydroxyproline in both collagen and elastin of aortae is then determined. In phase 2 castrated and non-castrated female rats will be treated with estradiol, progesterone, testosterone, contraceptive steroids, or oil and the same determinations will be done.